[HBASE-25826] Revisit the synchronization of balancer implementation

• Type: Umbrella
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-1, 2.5.0
• Component/s: Balancer

Release Note

Narrow down the public facing API for LoadBalancer by removing balanceTable and setConf methods.
Redesigned the initilization sequence to simplify the initialization code. Now all the setters are just 'setter', all the initialization work are moved to initialize method.
Rename setClusterMetrics to updateClusterMetrics, as it will be called periodically while other setters will only be called once before initialization.
Add javadoc for LoadBalancer class to mention how to do synchronization on implementation classes.

• Assignee: Duo Zhang
• Reporter: Duo Zhang
• Created: 29/Apr/21 08:03
• Updated: 17/May/21 02:43
• Resolved: 17/May/21 02:43

Description

In StochasticLoadBalancer, some methods are synchronized, for example, setClusterMetrics, setConf, balanceTable, etc.

What I can see is that, we have ConfigurationObserver support, so we need to make sure that the configuration updating does not effect the balance operation, so we need synchronization here. But do we support two balance operations at the same time? And what about other balancer implementations?

I think we need to make the synchronization more clearer.

Issue Links

• is related to: HBASE-25649 Complete the work on moving all the balancer related classes to hbase-balancer module

Sub-Tasks

• Remove balanceTable method from LoadBalancer interface: Resolved
• Make LoadBalancer not extend Configurable interface: Resolved
• Move all the intialization work of LoadBalancer implementation to initialize method: Resolved
• Add documentation for LoadBalancer about synchronization: Resolved
• The regionFinder and rackManager fields in BaseLoadBalancer should be volatile: Resolved